The invention relates to the field of data carrier or medium disks, which can be optically recorded and read, the information being recorded in the form of a perturbation of a radiation-sensitive coating, e.g. a thermosensitive coating.
An optical head may comprise a GaAs semiconductor laser, a lens for setting to infinity, one or two anamorphic prisms, a polarization splitting or separating cube, a quarter-wave plate, a deviating or reflecting mirror and a system of servomotors for focusing on to the disk and for tracking purposes.
The light beam emitted by the laser source after reflection on the reflecting mirror is focused by the focusing lens on to a predetermined track of the data carrier. This reflecting mirror permits radial dependence on the optical head. However, due to the rotation of the reflecting mirror about its axis, this beam is subject to pupil effects. It is in fact diaphragmed by the entrance pupil of the focusing lens.